MongoDB - How to filter document objects within array? - mongodb

Question

I have a problem with filtering fields(objects) from my document using find function.
Here is my db.collection.find(..) document:
{
"_id": BinData(3, "Uz+QwtoVMt7hjpqMrLxVhQ=="),
"name": "jeorge",
"permissions": [
{
"key": "group.staff",
"value": true,
"context": [
{ "key": "server", "value": "test" }
]
},
{
"key": "group.tester",
"value": true,
"context": [
{ "key": "server", "value": "test" }
]
},
{
"key": "test.test",
"value": true
},
{
"key": "group.default",
"value": true
},
{
"key": "group.helper",
"value": true
}
]
}
How can I filter my document in two ways?
a) Display only fields with nested context object.
b) Display only fields, which hasn't got nested context objects.
Also I need to check if parent's object property key contains string "group" as value (If not - skip it).
For situation b, I have tried this function, but it prints result with only the first matched element (based on mongodb's documentation).
db.collection.find(
{
"_id": BinData(3, "Uz+QwtoVMt7hjpqMrLxVhQ==")
},
{
"permissions": {
$elemMatch: {
"key": {
$regex: "group",
},
"value": true
}
}
}
);
Is it possible by single query? Thanks!

Answer 1

db.collection.aggregate([
{
$match: { _id: BinData(3, "Uz+QwtoVMt7hjpqMrLxVhQ==") }
},
{
$set: {
permissions: {
$filter: {
input: "$permissions",
as: "p",
cond: {
$and: [
"$$p.context",
{ $regexMatch: { input: "$$p.key", regex: "group" } }
]
}
}
}
}
}
])
mongoplayground
db.collection.aggregate([
{
$match: {
_id: BinData(3, "Uz+QwtoVMt7hjpqMrLxVhQ==")
}
},
{
$set: {
permissions: {
$filter: {
input: "$permissions",
as: "p",
cond: {
$and: [
{
$not: [ "$$p.context" ]
},
{
$regexMatch: {
input: "$$p.key",
regex: "group"
}
}
]
}
}
}
}
}
])
mongoplayground